This allows the execution time of basic operations, such as get () and put (), to remain constant even for large sets.

The treemap classes:

The tree map class implements the map interface by using a tree.

A tree map provides an efficient means of storing key/values pairs in the sorted order and allows rapid retrieval.

A tree map guarantees that its element will be sorted in ascending key order.

The linkedhashmap classes:

This class extends maps.

Linked hash map maintains a linked list of the entries in the map, in the order in which they were inserted. Thus, when iterating a linked hash map, the elements will be returned in the order in which they were inserted.

We can also create a linked hash map that returns its elements in the order in which they were last accessed.

The identify hash map class:

This class extends hash abstract map.

It is similar to the hash map except that it uses reference equality when comparing elements.

The java2 documentation explicitly states that identify hash map is not for general use.